Extend libdm_rust to build dm-crypt device

Add crypt module which supports building DmCryptTarget based dm table
entry. Also expose this via create_crypt_device()

Also, add unit test that use loopdevice as the backing device.

Test: atest libdm_rust.test
Bug: 250880499
Change-Id: Ibf09ca267cbcc7a2dc00dd835f2d8b781040f130

libs/devicemapper/Android.bp

@@ -36,5 +36,5 @@ rust_test {
         "libscopeguard",
         "libtempfile",
     ],
-    data: ["tests/data/*"],
+    data: ["testdata/*"],
 }

libs/devicemapper/src/crypt.rs

@@ -0,0 +1,153 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/// `crypt` module implements the "crypt" target in the device mapper framework. Specifically,
+/// it provides `DmCryptTargetBuilder` struct which is used to construct a `DmCryptTarget` struct
+/// which is then given to `DeviceMapper` to create a mapper device.
+use crate::util::*;
+use crate::DmTargetSpec;
+
+use anyhow::{bail, Context, Result};
+use data_model::DataInit;
+use std::io::Write;
+use std::mem::size_of;
+use std::path::Path;
+
+const SECTOR_SIZE: u64 = 512;
+
+// The UAPI for the crypt target is at:
+// Documentation/admin-guide/device-mapper/dm-crypt.rst
+
+/// Supported ciphers
+pub enum CipherType {
+    // TODO(b/253394457) Include ciphers with authenticated modes as well
+    AES256XTS,
+}
+
+pub struct DmCryptTarget(Box<[u8]>);
+
+impl DmCryptTarget {
+    /// Flatten into slice
+    pub fn as_slice(&self) -> &[u8] {
+        self.0.as_ref()
+    }
+}
+
+pub struct DmCryptTargetBuilder<'a> {
+    cipher: CipherType,
+    key: Option<&'a [u8]>,
+    iv_offset: u64,
+    device_path: Option<&'a Path>,
+    offset: u64,
+    device_size: u64,
+    // TODO(b/238179332) Extend this to include opt_params, in particular 'integrity'
+}
+
+impl<'a> Default for DmCryptTargetBuilder<'a> {
+    fn default() -> Self {
+        DmCryptTargetBuilder {
+            cipher: CipherType::AES256XTS,
+            key: None,
+            iv_offset: 0,
+            device_path: None,
+            offset: 0,
+            device_size: 0,
+        }
+    }
+}
+
+impl<'a> DmCryptTargetBuilder<'a> {
+    /// Sets the device that will be used as the data device (i.e. providing actual data).
+    pub fn data_device(&mut self, p: &'a Path, size: u64) -> &mut Self {
+        self.device_path = Some(p);
+        self.device_size = size;
+        self
+    }
+
+    /// Sets the encryption cipher.
+    pub fn cipher(&mut self, cipher: CipherType) -> &mut Self {
+        self.cipher = cipher;
+        self
+    }
+
+    /// Sets the key used for encryption. Input is byte array.
+    pub fn key(&mut self, key: &'a [u8]) -> &mut Self {
+        self.key = Some(key);
+        self
+    }
+
+    /// The IV offset is a sector count that is added to the sector number before creating the IV.
+    pub fn iv_offset(&mut self, iv_offset: u64) -> &mut Self {
+        self.iv_offset = iv_offset;
+        self
+    }
+
+    /// Starting sector within the device where the encrypted data begins
+    pub fn offset(&mut self, offset: u64) -> &mut Self {
+        self.offset = offset;
+        self
+    }
+
+    /// Constructs a `DmCryptTarget`.
+    pub fn build(&self) -> Result<DmCryptTarget> {
+        // The `DmCryptTarget` struct actually is a flattened data consisting of a header and
+        // body. The format of the header is `dm_target_spec` as defined in
+        // include/uapi/linux/dm-ioctl.h.
+        let device_path = self
+            .device_path
+            .context("data device is not set")?
+            .to_str()
+            .context("data device path is not encoded in utf8")?;
+
+        let key =
+            if let Some(key) = self.key { hexstring_from(key) } else { bail!("key is not set") };
+
+        // Step2: serialize the information according to the spec, which is ...
+        // DmTargetSpec{...}
+        // <cipher> <key> <iv_offset> <device path> \
+        // <offset> [<#opt_params> <opt_params>]
+        let mut body = String::new();
+        use std::fmt::Write;
+        write!(&mut body, "{} ", get_kernel_crypto_name(&self.cipher))?;
+        write!(&mut body, "{} ", key)?;
+        write!(&mut body, "{} ", self.iv_offset)?;
+        write!(&mut body, "{} ", device_path)?;
+        write!(&mut body, "{} ", self.offset)?;
+        write!(&mut body, "\0")?; // null terminator
+
+        let size = size_of::<DmTargetSpec>() + body.len();
+        let aligned_size = (size + 7) & !7; // align to 8 byte boundaries
+        let padding = aligned_size - size;
+
+        let mut header = DmTargetSpec::new("crypt")?;
+        header.sector_start = 0;
+        header.length = self.device_size / SECTOR_SIZE; // number of 512-byte sectors
+        header.next = aligned_size as u32;
+
+        let mut buf = Vec::with_capacity(aligned_size);
+        buf.write_all(header.as_slice())?;
+        buf.write_all(body.as_bytes())?;
+        buf.write_all(vec![0; padding].as_slice())?;
+
+        Ok(DmCryptTarget(buf.into_boxed_slice()))
+    }
+}
+
+fn get_kernel_crypto_name(cipher: &CipherType) -> &str {
+    match cipher {
+        CipherType::AES256XTS => "aes-xts-plain64",
+    }
+}

libs/devicemapper/src/lib.rs

@@ -38,6 +38,8 @@ use std::mem::size_of;
 use std::os::unix::io::AsRawFd;
 use std::path::{Path, PathBuf};
 
+/// Exposes DmCryptTarget & related builder
+pub mod crypt;
 /// Expose util functions
 pub mod util;
 /// Exposes the DmVerityTarget & related builder
@@ -46,9 +48,10 @@ pub mod verity;
 pub mod loopdevice;
 
 mod sys;
+use crypt::DmCryptTarget;
 use sys::*;
 use util::*;
-use verity::*;
+use verity::DmVerityTarget;
 
 nix::ioctl_readwrite!(_dm_dev_create, DM_IOCTL, Cmd::DM_DEV_CREATE, DmIoctl);
 nix::ioctl_readwrite!(_dm_dev_suspend, DM_IOCTL, Cmd::DM_DEV_SUSPEND, DmIoctl);
@@ -151,27 +154,55 @@ impl DeviceMapper {
         Ok(DeviceMapper(f))
     }
 
-    /// Creates a device mapper device and configure it according to the `target` specification.
+    /// Creates a (crypt) device and configure it according to the `target` specification.
+    /// The path to the generated device is "/dev/mapper/<name>".
+    pub fn create_crypt_device(&self, name: &str, target: &DmCryptTarget) -> Result<PathBuf> {
+        self.create_device(name, target.as_slice(), uuid("crypto".as_bytes())?, true)
+    }
+
+    /// Creates a (verity) device and configure it according to the `target` specification.
     /// The path to the generated device is "/dev/mapper/<name>".
     pub fn create_verity_device(&self, name: &str, target: &DmVerityTarget) -> Result<PathBuf> {
+        self.create_device(name, target.as_slice(), uuid("apkver".as_bytes())?, false)
+    }
+
+    /// Removes a mapper device.
+    pub fn delete_device_deferred(&self, name: &str) -> Result<()> {
+        let mut data = DmIoctl::new(name)?;
+        data.flags |= Flag::DM_DEFERRED_REMOVE;
+        dm_dev_remove(self, &mut data)
+            .context(format!("failed to remove device with name {}", &name))?;
+        Ok(())
+    }
+
+    fn create_device(
+        &self,
+        name: &str,
+        target: &[u8],
+        uid: String,
+        writable: bool,
+    ) -> Result<PathBuf> {
         // Step 1: create an empty device
         let mut data = DmIoctl::new(name)?;
-        data.set_uuid(&uuid("apkver".as_bytes())?)?;
+        data.set_uuid(&uid)?;
         dm_dev_create(self, &mut data)
             .context(format!("failed to create an empty device with name {}", &name))?;
 
         // Step 2: load table onto the device
-        let payload_size = size_of::<DmIoctl>() + target.as_slice().len();
+        let payload_size = size_of::<DmIoctl>() + target.len();
 
         let mut data = DmIoctl::new(name)?;
         data.data_size = payload_size as u32;
         data.data_start = size_of::<DmIoctl>() as u32;
         data.target_count = 1;
-        data.flags |= Flag::DM_READONLY_FLAG;
+
+        if !writable {
+            data.flags |= Flag::DM_READONLY_FLAG;
+        }
 
         let mut payload = Vec::with_capacity(payload_size);
         payload.extend_from_slice(data.as_slice());
-        payload.extend_from_slice(target.as_slice());
+        payload.extend_from_slice(target);
         dm_table_load(self, payload.as_mut_ptr() as *mut DmIoctl)
             .context("failed to load table")?;
 
@@ -185,15 +216,6 @@ impl DeviceMapper {
         wait_for_path(&path)?;
         Ok(path)
     }
-
-    /// Removes a mapper device
-    pub fn delete_device_deferred(&self, name: &str) -> Result<()> {
-        let mut data = DmIoctl::new(name)?;
-        data.flags |= Flag::DM_DEFERRED_REMOVE;
-        dm_dev_remove(self, &mut data)
-            .context(format!("failed to remove device with name {}", &name))?;
-        Ok(())
-    }
 }
 
 /// Used to derive a UUID that uniquely identifies a device mapper device when creating it.
@@ -208,3 +230,113 @@ fn uuid(node_id: &[u8]) -> Result<String> {
     let uuid = Uuid::new_v1(ts, node_id)?;
     Ok(String::from(uuid.to_hyphenated().encode_lower(&mut Uuid::encode_buffer())))
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crypt::DmCryptTargetBuilder;
+    use std::fs::{read, File, OpenOptions};
+    use std::io::Write;
+
+    const KEY: &[u8; 32] = b"thirtytwobyteslongreallylongword";
+    const DIFFERENT_KEY: &[u8; 32] = b"drowgnolyllaergnolsetybowtytriht";
+
+    // Create a file in given temp directory with given size
+    fn prepare_tmpfile(test_dir: &Path, filename: &str, sz: u64) -> PathBuf {
+        let filepath = test_dir.join(filename);
+        let f = File::create(&filepath).unwrap();
+        f.set_len(sz).unwrap();
+        filepath
+    }
+
+    fn write_to_dev(path: &Path, data: &[u8]) {
+        let mut f = OpenOptions::new().read(true).write(true).open(&path).unwrap();
+        f.write_all(data).unwrap();
+    }
+
+    fn delete_device(dm: &DeviceMapper, name: &str) -> Result<()> {
+        dm.delete_device_deferred(name)?;
+        wait_for_path_disappears(Path::new(MAPPER_DEV_ROOT).join(&name))?;
+        Ok(())
+    }
+
+    #[test]
+    fn mapping_again_keeps_data() {
+        // This test creates 2 different crypt devices using same key backed by same data_device
+        // -> Write data on dev1 -> Check the data is visible & same on dev2
+        let dm = DeviceMapper::new().unwrap();
+        let inputimg = include_bytes!("../testdata/rand8k");
+        let sz = inputimg.len() as u64;
+
+        let test_dir = tempfile::TempDir::new().unwrap();
+        let backing_file = prepare_tmpfile(test_dir.path(), "storage", sz);
+        let data_device = loopdevice::attach(
+            backing_file,
+            0,
+            sz,
+            /*direct_io*/ true,
+            /*writable*/ true,
+        )
+        .unwrap();
+        scopeguard::defer! {
+            loopdevice::detach(&data_device).unwrap();
+            _ = delete_device(&dm, "crypt1");
+            _ = delete_device(&dm, "crypt2");
+        }
+
+        let target =
+            DmCryptTargetBuilder::default().data_device(&data_device, sz).key(KEY).build().unwrap();
+
+        let mut crypt_device = dm.create_crypt_device("crypt1", &target).unwrap();
+        write_to_dev(&crypt_device, inputimg);
+
+        // Recreate another device using same target spec & check if the content is the same
+        crypt_device = dm.create_crypt_device("crypt2", &target).unwrap();
+
+        let crypt = read(crypt_device).unwrap();
+        assert_eq!(inputimg.len(), crypt.len()); // fail early if the size doesn't match
+        assert_eq!(inputimg, crypt.as_slice());
+    }
+
+    #[test]
+    fn data_inaccessible_with_diff_key() {
+        // This test creates 2 different crypt devices using different keys backed
+        // by same data_device -> Write data on dev1 -> Check the data is visible but not the same on dev2
+        let dm = DeviceMapper::new().unwrap();
+        let inputimg = include_bytes!("../testdata/rand8k");
+        let sz = inputimg.len() as u64;
+
+        let test_dir = tempfile::TempDir::new().unwrap();
+        let backing_file = prepare_tmpfile(test_dir.path(), "storage", sz);
+        let data_device = loopdevice::attach(
+            backing_file,
+            0,
+            sz,
+            /*direct_io*/ true,
+            /*writable*/ true,
+        )
+        .unwrap();
+        scopeguard::defer! {
+            loopdevice::detach(&data_device).unwrap();
+            _ = delete_device(&dm, "crypt3");
+            _ = delete_device(&dm, "crypt4");
+        }
+
+        let target =
+            DmCryptTargetBuilder::default().data_device(&data_device, sz).key(KEY).build().unwrap();
+        let target2 = DmCryptTargetBuilder::default()
+            .data_device(&data_device, sz)
+            .key(DIFFERENT_KEY)
+            .build()
+            .unwrap();
+
+        let mut crypt_device = dm.create_crypt_device("crypt3", &target).unwrap();
+
+        write_to_dev(&crypt_device, inputimg);
+
+        // Recreate the crypt device again diff key & check if the content is changed
+        crypt_device = dm.create_crypt_device("crypt4", &target2).unwrap();
+        let crypt = read(crypt_device).unwrap();
+        assert_ne!(inputimg, crypt.as_slice());
+    }
+}

libs/devicemapper/src/util.rs

@@ -37,6 +37,21 @@ pub fn wait_for_path<P: AsRef<Path>>(path: P) -> Result<()> {
     Ok(())
 }
 
+/// Wait for the path to disappear
+#[cfg(test)]
+pub fn wait_for_path_disappears<P: AsRef<Path>>(path: P) -> Result<()> {
+    const TIMEOUT: Duration = Duration::from_secs(1);
+    const INTERVAL: Duration = Duration::from_millis(10);
+    let begin = Instant::now();
+    while !path.as_ref().exists() {
+        if begin.elapsed() > TIMEOUT {
+            bail!("{:?} not disappearing. TIMEOUT.", path.as_ref());
+        }
+        thread::sleep(INTERVAL);
+    }
+    Ok(())
+}
+
 /// Returns hexadecimal reprentation of a given byte array.
 pub fn hexstring_from(s: &[u8]) -> String {
     s.iter().map(|byte| format!("{:02x}", byte)).reduce(|i, j| i + &j).unwrap_or_default()